This invention relates to the field of medical devices, and more particularly to a guidewire for advancing a catheter within a body lumen in a procedure such as percutaneous transluminal coronary angioplasty (PTCA).
Catheters are generally elongated tubular devices for performing a variety of functions, and include operative catheters, such as angioplasty catheters, and guiding catheters such as those used for the introduction of operative devices or fluids to various locations within a patient's body. Many catheters are generally too flexible to be advanced unassisted and therefore are used with a guiding means such as a guidewire. For example, in a typical PTCA procedure a guiding catheter having a preformed distal tip is percutaneously introduced into the cardiovascular system of a patient in a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is then advanced through the guiding catheter either by itself or together with a dilatation catheter having an inflatable balloon on the distal portion thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guidewire crosses a lesion to be dilated, then the dilatation catheter is advanced into the patient's coronary anatomy until the balloon is properly positioned across the lesion. Once in position across the lesion, the balloon is inflated to dilate the stenosed region and open up the lumen of the artery. The dilatation catheter may then be removed following deflation of the balloon.
Conventional guidewires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. The distal extremity of the guidewire usually is shapeable, so that when torque is applied to the proximal end of the guidewire outside of the patient as the guidewire is advanced there through, the shaped distal extremity can be steered through the patient's vascular system.
A major requirement for guidewires and other guiding members, whether solid wire or tubular members, is that they have sufficient strength to be pushed through a patient's vascular system or other body lumen, and be flexible enough to be maneuvered within the patient, without inflicting trauma to the patient's vessel or other body lumen through which they are advanced. At the same time, they must have sufficient structural integrity that portions of the guidewire do not break off while inside the patient. Efforts to produce a guidewire having optimum strength and flexibility have been hampered by the fact that the strength and flexibility requirements are diametrically opposed, in that an increase in one usually involves a decrease in the other.
Often while attempting to advance the guidewire though the patient's vasculature, the guidewire and catheter combination will prove to have insufficient strength or flexibility to be fully advanced. For example, a relatively flexible guidewire is best suited for the initial advancement within the vessel, while a guidewire with less flexibility is needed to continue advancement once the guidewire is deep within the patient. Therefore, it can become necessary for the physician to exchange the guidewire to complete the advancement. However, in order to exchange a guidewire, the access achieved by the guidewire within the patient's vasculature must be sacrificed, and the time consuming process of advancing a replacement guidewire must be performed. In addition to increasing the duration of the procedure, the exchange increases the risk of trauma to the patient's vasculature from guidewire impact on the vessel wall.
Attempts to produce guidewires that are adaptable to different situations inside the patient's lumen, which thereby avoid exchange of the guidewire after introduction into the patient, include guidewires made of pseudoelastic or shape memory material and moveable core guidewires. Moveable core guidewires generally have a solid inner core that can be moved in and out of a flexible distal end coil, to thereby change the flexibility of the distal end of the guidewire. It has been found that because the solid core is generally significantly less flexible than the distal end, the core is prone to piercing through the flexible distal end coil during advancement of the solid core. Guidewires made from pseudoelastic and/or shape memory materials such as NITINOL (NiTi alloy) generally have a tensile strength and/or shape which can be changed in response to a change in restraining force or temperature while the guidewire is inside the body. For example, pseudoelastic, shape memory alloys generally have at least two phases, a martensite phase, which has a relatively low tensile strength and which is stable at relatively low temperatures, and an austenite phase, which has a relatively high tensile strength and which is stable at temperatures higher than the martensite phase. A switch from one phase to the other will change the strength and possibly the shape of the material. While inside the patient, a guidewire made from these alloys may undergo one permanent phase change with a corresponding change in strength or shape, or may possibly cycle between two phases. However, like the moveable core guidewire, pseudoelastic shape memory alloy guidewires provide only limited procedural flexibility to the physician, in that guidewires produced using such techniques possess only one or two strength or shape options that the physician may change between during use.
Attempts at producing one guidewire with optimum strength and flexibility for the multitude of situations encountered within a patient's lumen have proven unsuccessful. What has been needed is a guidewire which is easily adaptable to any situation within a patient's lumen, to provide procedural flexibility while minimizing cost and procedural complexity.